Many mass flow controllers (MFC) control the flow rate of a gas flowing through the controller using a flow sensor. One type of flow sensor measures the actual flow rate of the gas flowing through the controller and based on a difference between the actual flow rate (as measured by the flow sensor) and a desired flow rate (as set by a user), a control signal is sent to a MFC valve. The MFC valve may receive the control signal and adjust the valve to increase or decrease the flow rate in order for the actual flow rate to more closely equal the desired flow rate.
At times, it is necessary to quickly change the control signal provided to the valve due to quickly changing flow conditions. For example, it may be necessary to rapidly adjust the valve displacement during a period of rapidly changing gas pressure or to adjust the valve displacement when it is necessary to quickly change the flow rate of the gas flowing through the MFC. During a period where a rapid change of the valve displacement is required, the flow sensor may be unable to provide the data necessary to accurately adjust the flow rate.
In order to more accurately adjust the valve during periods of rapidly changing flow conditions, an MFC feed-forward-mode may be implemented. During a feed-forward-mode, a signal may be emitted from a MFC pressure sensor to the valve. The valve may utilize the pressure sensor signal, or a modified version of the signal, to adjust the gas flow rate.